Centralizers are commonly used in oil and gas wellbore installations and generally serve to center a pipe or casing within a wellbore or previous casing string during run-in, installation, or cementing procedures. Conventional centralizers typically are characterized by a pair of opposed stop collars or stop rings with a number of outwardly-bowed springs extending longitudinally there between to contact the wellbore sidewalls and exert a centering force on the pipe or casing segment. Bow spring centralizer subs generally comprise a casing segment with pin and box connections and an integral bow spring centralizer. The centralizer sub is run as part of a casing string.
In under-reamed applications, the casing string (with centralizers) is passed through a smaller casing string (restriction) before opening up to a larger hole. Significant force is required to compress a bow spring centralizer and push it through a restriction. As drilling projects push to greater and greater depths, increased drilling angles, and through a greater variety of geological formations, more challenging demands are placed on centralizers and other down-bore equipment. For example, deeper wells require more stages and passage of centralizers through a greater range and number of corresponding restrictions.
Subjecting compressible bow strings to varied and varying pressures as it is passed down a well results in inconsistent, imperfectly predictable, and repeated strains.
Conventional bow springs can therefore suffer from a number of disadvantages in such installations. As the bore restrictions become tighter, the starting or insertion force and running forces required to pass restrictions increase. Additionally, compression of the bow springs through particularly tight restrictions can exceed the elastic range of the material, can lead to deformation of bow springs, and compromise the ability of the bow springs to restore and to center. Similarly, damaged or forced centralizers can damage down-bore surfaces and down-bore equipment. The repeated compressions and decompressions of the bow springs of the centralizers compromise the integrity and reliability of the centralizer.
Accordingly, the following discloses and enables improvements for reducing and controlling insertion forces and running forces and preserving centralizer integrity and down-bore surfaces and equipment against the increasing demands of deep-well drilling.